Differential area compressor bleed control



Jan. 24, 1956 L. E. RUBY DIFFERENTIAL AREA COMPRESSOR BLEED CONTROL Filed Oct. 17, 1952 INVENTOR LOWELL E. RUB)" sm ma yfiwk AGENT 2,732,125 DIFFERENTIAL AREA C OIlYI PRESSOR BLEED' Application October 17, 1952-, Serial No. 315,289

6 Claims. (Cl. 230-115) This invention relates to fiowcompressors, more particularly to controls for bleeding axial flow compressors.

Compressors of the axial flow type are made up of a plurality of bladed stages whichact to increase the pressure of gases flowing through the compressor, each succeeding stage further compressing the-gases. By varying the number of stages, the pressure ratio, that is the ratio of compressor discharge pressure to compressor inlet pressure, can be controlled. A detrimental characteristicv of axial flow compressors is a tendency to surge or pulsatev at low speeds, sometimes resulting in physical damage to the compressor or its associated structure. This characteristic is due to the fact that the various stages. of the compressor are: designed. for maximum efiicieney as a unit at one particular compressor speed. At a speed lower than the design speed the various stages are not correctly matched for the volume of air flowing through the compressor. The tendency is for the first stages to overpump the latter stages with the result that the first stages stall out and cause surging or pulsating of the compressor.

The speed at which an axial flow gas turbine power plant can be started is below the design speed of its compressor and, consequently, starting is very difiicult if surge or pulsation exists. It is known that by" bleeding the compressor the operating characteristics of the compressor can be changed and the detrimental characteristic overcome. More is gained in compressor performance than is lost by dumping or wasting the gases which have been compressed and had work done on them.

Various methods have been used for bleeding axial flow compressors and for controlling the bleeding thereof. The subject of this invention is a differential area control which controls bleeding as a function of compressor pressure ratio. This ratio changes with a change in compressor speed, but it remains substantially constant: with an increase in altitude. Consequently, the only working fluid employed by the control is compressor air, and altitude correction features are not required.

An object of the invention is to provide an. axial flow compressor bleed control which is relatively simple and which provides dependable operation.

Another object of the invention is to provide an axial flow compressor bleed control which provides gradual closing of the bleeds over a given speed range so as to obtain maximum performance from the. compressor.

Other objects and advantages will. be apparent from the specification and claims, and from the. accompanying drawing which illustrates an embodiment of the invention.

In the drawing, the single figure illustrates an axial flow gas turbine power plant having the compressor bleed control connected thereto.

Referring to the drawing in detail, 10 indicates. anaxial flow gas turbine power plant having inlet 12,, compressor section 14, combustion section 16, turbine section 18 and:

' United States Patent O exhaust nozzle 20. The compressor section is surroundedby casing .22 and has mounted therein rotor 24 comprised of a plurality of discs 26, each disc having blades. 28 about its periphery. Interspaced between each row of. rotor blades 28 are rows of stator vanes- 30 which serve to turn the gases flowing through the compressor so that they strike the succeeding rotor blades 28' at the most efiic'ient angle. The compressor illustrated is a thirteen.- stage compressor but it is to be understood that it can be comprised of any suitable number of stages.

Compressor casing 22 is surrounded by wall 32 which together with the casing defines annular manifold 34. The compressor is vented to the manifold as by one or more ports 36 immediately downstream of the sixth compressor stage, although any convenient stage: of the compressor may be picked for locating the bleed port 1 stantially larger than the area of face 52 onland 48.

.lected because it is a convenient norm.

The left end of bleed control 38 is connected by line 54 to the same compressor stage to which manifold 34 is vented, one end of the linebeing mounted within port 36. In this way sixth stage compressor pressure is ducted to chamber 56 adjacent to. land face 50. Line 54 has a branch 58 extending into manifold 34 through which the pressure in the manifold also is ducted to chamber 56, the pressure in the latter chamber being in effect an average of the pressure at the sixth stage of the compressor and that in manifold 34. The right end of bleed control 38" is shown connected by line 60 to a port at the discharge end of the compressor so that compressor discharge pressure is ducted through the line to chamber 62 adjacent to land face 52.

Lands 46 and 48 have a chamber 64' therebetween which is connected to compressor inlet pressure through ports 66 and groove 68 in sleeve 42, and line 70. While chamber 64 can be connected to some other compressor stage pressure, compressor inlet pressure has been se- A second set of ports 72 in sleeve 42 are connected through groove 74, also in sleeve 42, and line 76 to chamber 78 adjacent to bleed shut-ofif piston 80; The bleed shut-off piston. is contained in housing 82, mounted in wall 32, and controls the area of bleed ports 84 in the housing through which compressor air' is bled to the. atmosphere or to any desired receiver. Line 76 has an extension 86 for connecting the line with any additional number of bleed shut-off pistons disposed around the power plant, only one being shown here for convenience.

In operation the compressor bleed control works as follows: The power plant is started and as compressor speedis increased, compressor discharge pressure acting. upon land face 52 increases at a faster rate than the combination of sixth stage static pressure and the pres sure in manifold 34, which pressures act upon land face 50. This causes piston. 44. to move to the left to par tially uncover ports 72 and admit compressor discharge pressure through line. 76 tothe top of bleed shut-off piston, or pistons, 80. This pressure: forces the bleed shut-oh piston downward to restrict bleed port 84, reducing the volume. of gases bled and increasing the pressurewithin manifold 34. This increased manifold pressure acts upon land face 50; to restrain movement to the left of piston 44 and finally the system achieves a balance 3 with bleed shut-off piston 80 partially closing bleed port 84.

As compressor speed further increases, compressor discharge pressure increases at a faster rate than the new sixth stage compressor pressure and manifold pressure 34 and piston 44 moves to a new balanced position with the bleed port 84 further closed. This relationship continues as compressor speed increases until bleed port 84 is completely closed, piston 44 having moved to the left sulficiently far to fully uncover ports 72. As should be evident, a gradual closing of the bleed openings is obtained. The control can be designed so that bleeding is terminated at any particular compressor speed.

Expressing operation in another sense, when the pressure ratio Compressor discharge-compressor inlet Compressor intermediate, manifold-compressor inlet equals or exceeds area ratio Land 46 Land 52 Compressor discharge pressure-compressor inlet pressure Compressor intermediate pressure-compressor inlet pressure equals the area ratio of Land 46 Land 52 the bleed openings will be completely closed.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from the spirit as defined by the following claims:

I claim:

l. A multi-stage axial flow compressor having means for bleeding an intermediate stage thereof and means for regulating flow through said bleeding means in combination with a bleed control comprising a housing containing a differential area piston capable of reciprocal motion therein, means subjecting one end of said piston to compressor discharge pressure and the other end to the pressure at the intermediate compressor stage being bled so that said piston is moved as a function of compressor pressure ratio, and means controlled by motion of said piston for admitting compressor discharge pressure to said flow regulating means to actuate said flow regulating means and control compressor bleeding.

2. A multi-stage axial flow compressor having at least one bleed port for bleeding an intermediate stage of the compressor and at least one valve for regulating flow through said port in combination with a bleed control comprising a housing containing a differential area piston capable of reciprocal motion therein, means subjecting one end of said piston to compressor discharge pressure and the other end to the pressure at the intermediate compressor stage being bled so that said piston is moved as a function of compressor pressure ratio, and means controlled by motion of said piston for admitting compressor discharge pressure to said valve to progressively close said valve as compressor speed increases.

3. A bleed control for a multi-stage axial flow compressor in a gas turbine power plant, said control including a chamber surrounding the compressor, said chamber being vented to an intermediate stage of the compressor, a port in said chamber through which compressor gases in the chamber can be bled, means regulating the area of said bleed port, a housing having a differential area piston therein, capable of reciprocal motion, means subjecting the larger end of said piston to the pressure within said chamber as well as to the pressure at the intermediate compressor stage to which said chamber is vented, means subjecting the smaller end of said piston to compressor discharge pressure, and means controlled by motion of said piston for admitting compressor discharge pressure to said bleed area regulating means to regulate said bleed port as a function of compressor pressure ratio.

4. A bleed control for a multi-stage axial flow compressor in a gas turbine power plant, said control including a chamber surrounding the compressor, said chamber being vented to an intermediate stage of the compressor, a port in said chamber through which compressor gases in the chamber can be bled, valve means regulating the area of said bleed port, a housing having a slidable piston therein capable of reciprocal motion, one end of said piston having a larger surface area than the opposite end, means subjecting the larger area end to the pressure within said chamber and also to the pressure at the compressor intermediate stage to which said chamber is vented, means subjecting the opposite end to compressor discharge pressure, a groove around said piston and between said ends, means venting said groove to compressor inlet pressure, and means controlled by motion of said control piston for admitting compressor discharge pressure to said valve to actuate said valve and regulate said bleed port as a function of compressor pressure ratio.

5. A bleed control for a multi-stage axial flow compressor in a gas turbine power plant, said control including a chamber surrounding the compressor, said chamber being vented to an intermediate stage of the compressor, a port in said chamber through which compressor gases in the chamber can be bled, valve means regulating the area of said bleed port, a housing defining a cylinder having a slidable control piston therein capable of reciprocal motion, one end of said control piston having a larger surface area than the opposite end, a connection between the compressor intermediate stage to which said chamber is vented and said housing cylinder through which the larger area end of said piston is subjected to the pressure at said compressor intermediate stage, a connection between said chamber and said housing cylinder through which said larger area end is also vented to the pressure within said chamber, a connection between compressor discharge and said housing cylinder through which the opposite end of said control piston is vented to compressor discharge pressure, a groove around said control piston and between said ends, a connection between compressor inlet and said housing cylinder for venting said groove to compressor inlet pressure, and means controlled by motion of said piston for admitting compressor discharge pressure to said valve means to actuate said valve and regulate said bleed port as a function of compressor pressure ratio.

6. A bleed control for a multi-stage axial flow compressor in a gas turbine power plant, said control including a chamber surrounding the compressor, said chamber being vented to an intermediate stage of the compressor, a plurality of ports in said chamber through which compressor gases in the chamber can be bled, valve means regulating the area of said bleed ports, a housing defining a cylinder having a slidable control piston therein capable of reciprocal motion, one end of said control piston hav ing a larger surface area than the opposite end, a connection between the compressor intermediate stage to which said chamber is vented and said housing cylinder through which the larger area end of said piston is subjected to said pressure at the compressor intermediate stage, a connection between said chamber and said housing cylinder through which said larger area end is also vented to said pressure within said chamber, a connection between compressor discharge and said housing cylinder through which the opposite end of said control piston is vented to compressor discharge pressure, a groove around said control piston and between said ends, a connection between compressor inlet and said housing cylinder for venting said 'groove to compressor inlet pressure, and' means controlled by motion of said control piston for admitting compressor discharge pressure to said valve means to actuate said valve and regulate said bleed ports as a function of compressor pressure ratio.

References Cited in the file of this patent UNITED STATES PATENTS Clark et a1. Apr. 16, 1946 Borden Nov; 30, 1948 FOREIGN PATENTS Great Britain Mar. 28, 1947 

